Method of producing vanthoffite



Sept- 13, 1960 w. B. DANCY 2,952,515

METHOD OF PRODUCING VANTHOFFITE f Filed Oct. 8, 1958 tates 2,952,515 METHOD F PRODUCING VANTHOFFITE Filed oct. s, i953, ser. No. 766,075 s Claims. (ci. 'z3- 121) This invention relates to the production of sodium sulfate. More particularly, it relates to the production of sodium sulfate via vanthoite from magnesium sulfate.

The art shows Various methods for producing sodium sulfate, many of which require costly materials and/ or elaborate processes. One such method involves the production of sodium sulfate by treating sodium chloride with sulfur dioxide, air, and steam at a temperature between about 400 and about 450 C. with the aid of a catalyst such as ferric or cupric oxide (British Patent Nos, 3045 and 3047 (1870)). In this procedure the presence of a reactive gas is required as well as a high temperature, necessitating large scale production of heat.

Another method comprises lthe heating of astrakanite (NagSOg-MgSOyfl-IZO) with carbon to a red glow, producing a mixture of sodium sulfate, magnesium oxide, sulfur dioxide and carbon monoxide (German Patent No. 368,935 (1921)). The end products, sulfur dioxide and carbon monoxide, produce hazardous operating conditions. Additional steps are required to remove the sodium sulfate from the reaction mixture.

A three-step method for the production of sodium sulfate is disclosed in United States Bureau of Mines Report of Investigations No. 3299, March 1936, wherein a solution of magnesium sulfate is commingled with so dium chloride and reacted at elevated temperatures around 75 C. to yield astrakanite The astrakanite is admixed with a solution containing sodium chloride and sodium sulfate, and allowed to re` act at about 107 C. to produce vanthoilte The vanthoite is reacted with sodium chloride at a temperature around 55 C. to yield sodium sulfate.

A11 object of the present invention is to provide an improved process for the production of vanthoiite.

Another object is to provide a one-step process for the production of vanthoilite from magnesium sulfate,

Another object is to provide a one-step process for the production of vanthote from potassium-magnesium double sulfates.

Another object is to provide a tion of potassium-free vanthoite.

Another object is to provide an improved, yet simple, process for the production of sodium sulfate by the efcient utilization of langbeinite, schoenite, leonite or other potassium-magnesium double sulfates.

Another object is to produce soditun sulfate from magnesium sulfate in a maximum of two conversion steps.

Another object is to provide an improved process for the production of sodium sulfate which produces commercially attractive yields and a product of high purity.

Still further objects and advantages of the present invention will be apparent from the following detailed description.

Vanthoflite is prepared in the present invention from process for the producmagnesium sulfate, mixtures of potassium and magnesium sulfates, and potassium and magnesium double sulfates, such as langbeinite (2MgSO4-K2SO4), schoenite (M gSO., K2SO4 6H2O) and leonite In accordance with the present invention, solid-phase vanthofiite, substantially potassium-free, is produced in a single step by reacting sodium chloride with magnesium sulfate or with `a mixture of potassium and magnesium sulfates in aqueous solution at a temperature above about C. and under other operating conditions more fully described below. The solid vanthoiiite is` separated from the product slurry, during which separation any potassium salts that may be present remain in solution and are separated thereby from the vanthoite.

The vanthotiite may then be readily converted into sodium sulfate in an advantageous manner by reaction with sodium chloride in aqueous solution at temperatures above about 35 C. The sodium sulfate product is obtained in high purity and in a yield approximating 100% of the sodium sulfate present in the vanthoflite. In a specific embodiment of the present invention langbeinite is dissolved in water `at about 80 C., the amount of Water being sufficient to dissolve substantially all of the sulfates. Slimes are removed from the solution in a thickener. The solution is then admixed with recycled sodium sulfate mother liquor and recycled secondary salts, comprised of sodium chloride with small proportions of potassium and magnesium `chlorides and sulfates, in amounts to produce a solution containing about 5 parts of magnesium and about 30 parts of chloride per 100 parts of Water. The mixture is stirred and allowed to react at a temperature of about C. for about l to 3 hours to produce solid vanthoiiite. The vanthoite is separated from the reaction mixture by centrifugal means, iiltr-ation, or the like, during which separation substantially all potassium values are removed in the liquid phase.

The vanthoite is commingled and reacted with sodium chloride brine from the langbeinite ore washing process and sodium sulfate mother liquor, the total reaction mixture containing about 3 parts of magnesium andabout 20 parts of chloride per 100 parts of Water. The mixture is 'allowed to react at a temperature of about 45 C. for about 3 to 4 hours to produce sodium sulfate as a solid phase. The sodium sulfate is separated from the reaction mixture by ltration, by centrifugal means, or the like, and washed ywith water, filtered, and dried to yield a high purity product.

In the preparation of vanthote according to the present invention, magnesium sulfate or a potassium-magnesium double salt comprised thereof is dissolved in water, suitably a-t a temperature between about 30 C. and `the boiling temperature of the resulting solution, preferably around 80 C. The magnesium content of the solution should be between about 35 and about 50 moles of magnesium per 1000 moles of Water, preferably about 43 moles. The resulting solution is thickened if necessary to remove any slimes therefrom as an underflow. The deslimed `solution is admixed with sodium chloride and Water in a proportion suicient to produce a mixture containing up to but not exceeding about 5 parts of magnesium per parts of water (equivalent to about 37 moles per 1000 moles of water) and up to but not exceeding about 30 parts of chloride per 100 parts of water (equivalent to about moles per 1000 moles of water). The potassium content of the mixture should also be limited, the maximum tolerable proportion being about 8 parts of potassium per 100 parts of water (equivalent to about 37 moles per 1000 moles of water).

The mixture is allowed to react with stirring at a temperature above labout 80 C., preferably about 95 C., to form Vanthoffite as a solid phase. About 2 to about 4 hours are generally suticient for the Vanthotiite reaction to reach substantial completion. The solid Vanthoftite is separated from the reaction product mixture by centrifugal means, during which separation any contaminating potassium is substantially completely removed in the liquid phase.

The vantho'ite is converted into sodium sulfate according to the following procedure. A sodium chloride brine, suitably obtained by washing langbeinite ore, is commingled with vanthofiite and optionally with a sodium sulfate mother liquor from a later stage of the process, the proportions being adjusted to produce a mixture containing magnesium in a ratio not greater than about 3 parts per 100 parts of water and chloride in a ratio not greater than yabout 20 parts per 100 parts of water. The mixture is stirred and allowed to react at a temperature between about 35 and about 55 C., preferably about 48 C. to form crystalline sodium sulfate. About 2 to about 4 hours are generally sufficient for the reaction to reach substantial completion.

The sodium sulfate is separated from the reaction mixture by centrifugal means. It is repulped with water, filtered and dried to yield sodium sulfate of high purity.

The present invention may be more fully understood from the following specific example, to be read in conjunction With the attached flowsheet, illustrating a continuous process designed to produce 363 tons of sodium sulfate per day.

Example Prewashed langbeinite (375 tons) containing 3.0% sodium chloride is ground to minus 200 mesh and slurried at 80 C. in water (736 tons), wherein most of the sulfates dissolve.

The slurry is thickened at between 75 and 80 C. to separate the slirnes therefrom. The slimes are withdrawn as an underfliow, washed in a tray-type washer, and sent to waste. The liquor from the tray washer is optionally recycled to the dissolving step to reduce the quantity of fresh water required and to make use of the materials dissolved therein.

The overiiow solution from the thickener is admixed with sodium sulfate mother liquor (1833 tons), having the following composition,

K Mg Na l S04 H2O K Mg Na Cl S04 H2O This mother liquor is treated as hereinafter described to yield secondary salts which are recycled to the vanthoiiite reaction, described above.

The Vanthoite is commingled with clarified saturated sodium chloride brine (1431 tons) from the langbeinite ore washing step, and with sodium sulfate wash iiquor (400 tons), having the following compositions respectively, in tons:

The resulting mixture is agitated for 2 hours at 45- 48 C., during which time sodium sulfate (527 tons) crystallizes in the formof the anhydrous salt.

The reaction mixture is centrifuged to separate the sodium sulfate from the mother liquor (1833 tons). The sodium sulfate is repulped in Water, filtered, washed with water, and dried. The product is sodium sulfate (363 tons) of high purity.

The vantholiite mother liquor (3024 tons) from the vantholiite centrifuge is further processed as follows: The liquor is evaporated until the liquid phase approaches saturation with potassium chloride. Secondary salts are precipitated thereby in a total quantity of 664 tons, having the following analysis, in tons:

K Mg Na Cl S04 HgO The secondary salts are separated by centrifugal means and recycled to the vanthoiite formation step. The secondary salts mother liquor, comprised largely of magnesium chloride and potassium chloride constitutes an excellent source of material for the production of magnesium oxide as taught in U.S. Patent 2,809,880 (Dancy- Gloss-Shaw, October 1957).

It is to be understood that the preceding description and example have been given for the purpose of illustration only and the scope of the invention is not limited thereto. Various adaptations and modiiications of this invention will be apparent from the foregoing description.

In accordance with the foregoing description, what is desired to be secured by Letters Patent is:

1. A one-step process for the production of Vanthoftite from magnesium sulfate which comprises commingling magnesium sulfate, sodium chloride, and water in amounts not exceeding about 5 parts of magnesium `and not exceeding about 30 parts of chloride per 100 parts of water, the proportions thereof being greater than the concentrations thereof present in a saturated solution of vanthote at the reaction temperature subsequently employed, allowing the mixture to react at a temperature above about C. until the conversion to vanthoite is substantially complete, and recovering the solid vanthoite from the resulting slurry.

2. A process for the production of vanthotiite which comprises oommingling potassium and magnesium sulfates, sodium chloride, and water in amounts not exceeding about 5 parts of magnesium, not exceeding about 30 parts of chloride, and not exceeding about 8 parts of potassium per parts of water, the proportions thereof being greater than the concentrations thereof present in a saturated solution of vanthoifite `at the reaction temperature subsequently employed, allowing the mixture to react at a temperature above about 80 C. until the conversion to vanthotiite is substantially complete, and recovering the solid Vanthoii'ite from the resulting slurry.

3. A process as in claim 2 wherein said potassium and magnesium sulfates are langbeinite.

4. A process as in claim 2 wherein said potassium and magnesium sulfates are schoenite.

5. A process as in claim 2 wherein said potassium and magnesium sulfates are leonite.

6. A process for thepproduction of a substantially potassium-free vanthoite from a mixture of potassium and magnesium sulfates which comprises commingling a mixture of magnesium and potassium sulfates, sodium chloride, and Water in amounts not exceeding about parts of magnesium, not exceeding about 30 parts of chloride `and not exceeding about S parts of potassium per 100 parts of water, the proportions thereof being greater than the concentrations thereof present in a saturated solution of vanthoftlte 'at the reaction temperature subsequently employed, allowing the mixture to react at a temperature between about 80 C. and the boiling point of the solution until the conversion to vanthotlte is substantially complete, and recovering the vanthoite as a solid from the resulting slurry, whereby the potassium is removed therefrom in the liquid phase.

7. A process as in claim 6 wherein said mixture is allowed to react at a temperature around 95 C.

8. A process for the production of a substantially potassium-free vanthote from a mixture of potassium and magnesium sulfates which comprises commingling a mixture of potassium and magnesium sulfates, sodium chloride, and water in amounts of about 5 parts of magnesium, about parts of chloride and less than about 8 parts of potassium per 100 parts of water, allowing the mixture to react at a temperature around C. for around 2 hours, thereby forming solid vanthote, and recovering said vanthoilte substantially potassium-free from the resulting slurry, whereby the potassium values in the reaction mixture are removed in the liquid phase.

References Cited in the lle of this patent Conley et al.: Anhydrous Sodium Sulphate from Saline Deposits or Brines by a Four-Stage Process, U.S. Bureau of Mines Report of Investigation No. 31299, 18 pages, March 1936. 

1. A ONE-STEP PROCESS FOR THE PRODUCTION OF VANTHOFFITE FROM MAGNESIUM SULFATE WHICH COMPRISES COMMINGLING MAGNESIUM SULFATE, SODIUM CHLORIDE, AND WATER IN AMOUNTS NOT EXCEEDING ABOUT 5 PARTS OF MAGNESIUM AND NOT EXCEEDING ABOUT 30 PARTS OF CHLORIDE PER 100 PARTS OF WATER, THE PROPORTIONS THEREOF BEING GREATER THAN THE CONCENTRATIONS THEREOF PRESENT IN A SATURATED SOLUTION OF VANTHOFFITE AT THE REACTION TEMPERATURE SUBSEQUENTLY EMPLOYED, ALLOWING THE MIXTURE TO REACT AT A TEMPERATURE ABOVE ABOUT 80*C. UNTIL THE CONVERSION TO VANTHOFFITE IS SUBSTANTIALLY COMPLETE, AND RECOVERING THE SOLID VANTHOFFITE FROM THE RESULTING SLURRY. 